Various hand held or portable lighting devices, including flashlights, are known in the art. Such lighting devices typically include one or more dry cell batteries or rechargeable batteries having positive and negative electrodes. The batteries are arranged electrically in series or parallel in a battery compartment or housing. The battery compartment contains the batteries and may also, in some instances, be used to hold the lighting device. An electrical circuit is established from a battery electrode or terminal through conductive means which are electrically coupled with a light source, such as a lamp bulb or a light emitting diode (“LED”). After passing through the light source, the electric circuit continues through conductive means that are electrically coupled to the light source, which in turn are in electrical contact with the other electrode or terminal of a battery. The circuit includes a switch to open or close the circuit. Actuation of the switch to close the electrical circuit enables current to pass through the lamp bulb, LED, or other light source and through the filament, in the case of an incandescent lamp bulb-thereby generating light.
It may be desirable to provide multiple modes of operation for different needs. For example, in addition to the normal “full power” or “standard power” mode, a momentary mode only keeping the flashlight on as long as a pushbutton is pushed by a user, and/or a blink mode providing a strobe light or a blinking in a certain sequence like an SOS mode can be implemented in a portable lighting device, such as a flashlight. In such a portable lighting device, the user selects the desired mode of operation by manipulation of a user interface, which can be a main switch. For example, when the portable lighting device is in the normal mode or the power save mode of operation, the portable lighting device may be transitioned to another mode of operation, such as an SOS mode, by manipulating the main switch to momentarily turn “off” and then turn back “on” the portable lighting device. In another lighting device, the main switch may be required to be depressed and held a certain period of time to cause the lighting device to index to the next operational mode. Another option might be multiple pressing of the main switch by a user within a certain time between pressing and releasing the main switch button. A portable lighting device that includes advanced functionality may also include an electronic power switch controlled by a microcontroller or microprocessor to provide the desired functionality.
Flashlights and other portable lighting devices have conventionally employed a mechanical power switch in the main power circuit of the flashlight to turn “on” and turn “off” the portable lighting device. When the user turns “on” the portable lighting device, the user typically presses down or otherwise manipulates the mechanical power switch to mechanically connect two contacts to close the switch and complete the power circuit, thereby allowing current to flow from the positive terminal of the batteries, through the light source and to the negative terminal of the batteries. When the user turns “off” the portable lighting device, the user again manipulates the mechanical switch to disconnect the two contacts of the switch and thereby open the switch and break the power circuit. The mechanical power circuit in such devices, therefore, acts as a conductor in completing the power circuit, and thus conducts current throughout the operation of the portable lighting device.
For example, in multi-mode electronic portable lighting devices, the various modes of operation may be selected by a user turning off the lighting device for less than a predetermined period of time, such as 1 to 2 seconds, and then turning the lighting device back on again. In response to this short turn off period, the lighting device indexes to the next mode.
A known design for flashlights is to divide the electrical circuit so that the circuit elements needed in the direct vicinity of the light source are provided in the head of the flashlight, while the parts of the circuit that belong to the control of the flashlight are accommodated in the tail of the flashlight, including the man-machine interface, for instance a pushbutton.
Typically, at least 2 circuits are necessary, namely the main power supply circuit providing electrical power to the light source and a control circuit that controls the electrical power supplied to the light source. For any light source, specifically if the light source is an LED, the current through the LED needs to be constant or at least somewhat constant to provide a relatively constant output of light. In addition, it may be desirable to adjust the current so that the electrical power consumed by the LED stays constant to the extent this is desired. For instance, it may sometimes be desirable to accept a minor drop in electrical power, indicating to the user that the battery is getting old rather than regulating the buck circuit such as to compensate in full for the drop in electrical energy and then have a flashlight shut down without any warning at some point in time.
Regulation is typically achieved by a well known buck converter that reduces the voltage from the DC power source to the voltage needed for operating the LED, for instance to reduce a battery voltage of 5 V to an LED operating voltage of 3.2V. Buck converters comprise a high frequency switch, for instance turning the battery power periodically on and off at a frequency of 600 kHz. The regulating performance is achieved by a pulse width modulation (PWM), meaning that the duty cycle of the high frequency switch is modulated by modulating the time during which the switch is closed in comparison to the time over which the switch is open over one opening-closing cycle of the switch. Opening and closing the switch is repeated periodically at a high frequency, for instance 600 kHz. During the time the high frequency switch is closed, an inductor is charged that is connected in series with the light source, and during the time the high frequency switch is closed the inductor discharges electrical energy through the light source.
For controlling the duty cycle, typically a control circuit including a DC to DC converter circuit and/or a microcontroller is provided and the current through the light source is measured and sent as an input signal into the microcontroller that controls directly the duty cycle of the high frequency switch. In a flashlight, this results in a variety of design problems, for instance:
1. The man-machine interface is located in the tail. Therefore, it is preferred to provide also the microcontroller in the tail. Otherwise, an electric circuit would be necessary for transmitting the commands from the user through a tail switch to wherever the microcontroller is provided within the flashlight.
2. The control circuit needs to be provided with power. When providing the control circuit in the tail of the flashlight, while the light source needs to be of course in the head of the flashlight, different electric circuits are needed, i.e. the battery power needs to be brought both to the head and to the tail. This requires relatively complex mechanical parts like spring probes, contacts, and a housing able to accommodate these parts. Also, it makes the flashlights less robust as the risk of failure generally rises the more parts and the more electrical contacts need to be functional.
3. Since the LED is in the head of the flashlight, it is not only difficult to measure the current through the LED in the head where relatively little space is provided, but it would also require still another circuit to send this signal back into the DC to DC converter and/or microcontroller in the tail of the flashlight.
The result in the prior art was to provide several spring probes that contact different contacts. Since only one spring probe can be aligned with the central axis of the portable lighting device, contact rings need to be provided that can be contacted by biasing the spring probes against these contact rings. For using standard batteries, one solution in the prior art was to provide a battery cassette and provide contact rings on the battery cassette, and to provide contact rings in the head and the tail of the flashlight that can be contacted by spring probes provided in the battery cassette. While this solution works reliably, it comes at the price of a more complex design and is not a preferred solution for heavy duty portable lighting devices such as in use by law enforcement and the military favoring simple designs.